1. Field of the Invention
The present invention relates to an OFDM receiving apparatus and an OFDM receiving method using one segment reception of terrestrial digital broadcasting.
2. Description of the Related Art
In terrestrial digital broadcasting, one segment reception towards cellular phones and personal digital assistants was started. With showing a parameter example of one segment reception in an actual condition, a modulation system is a QPSK, a guard interval ratio is 1/8, a convolution code is 2/3, and a bit rate is broadcast at 416 kbps.
Since one segment reception is broadcast using one central segment among 13 segments in a frequency band which the present television broadcasting stations have been already assigned, only one segment reception is performed to one station among the terrestrial digital television broadcasting stations.
A receiver dedicated for one segment reception has a characteristic that circuit scale is smaller than that of a 13 segment receiver by performing reception using only a part of a synchronized signal in the whole 13 segments so as to make receiving processing into the minimum, and consumed power can be also suppressed.
In the meantime, demands for two or more channels of simultaneous reception (e.g., requests of recording of a program on a different channel and diversity reception) have increased also in in-vehicle TVs and portable mobile receivers these days, and use of configuration of using a plurality of receivers so as to satisfy such demands ends up losing a valuable feature that circuit scale is small. In particular, in configuration of arranging a plurality of receivers, unless circuitry and circuit scale of a receiver change, whether in one segment or in 13 segments, a circuit increment of an error correction unit becomes conspicuous as the number of channels increases.
As a conventional data transmission system using a plurality of channels, there are some which transmit and receive a transport stream at a high bit rate requiring a wide band, even if it is a transmission line of a narrow band per channel, by performing transmission after dividing a high bit rate transport stream (TS) into a plurality of channels by a transport stream packet (TSP) (e.g., refer to Japanese Application Patent Laid-Open Publication No. 2002-344965).
There are some others which achieve an inexpensive receiver or TV set by receiving digital signals of carrier waves at several different frequencies with a plurality of tuners respectively, and demodulating a digital base band signal from the plurality of tuners in time division with one demodulator (e.g., refer to Japanese Patent Application Laid-Open Publication No. 2000-152106).
However, the ones described in Japanese Patent Application Laid-Open Publication Nos. 2002-344965 and 2000-152106 cannot receive two or more channels of one segment broadcasting signals in ground digital broadcasting simultaneously.
Furthermore, a conventional digital receiver including a one segment receiver has an issue that a channel change is not necessarily performed in an instant, but switching time (time from a tuner receiving a carrier wave to outputting it as TS data) is necessary, namely time for 2 to 4 seconds is required from a change performing operation to a next channel being outputted on a screen.